The present invention relates to barriers for preventing wood pest (e.g. termite and boring insect) access to wooden structures for the long-term protection of wooden structures. More particularly, it relates to a composition and method which creates and maintains an exclusion zone for insect pests such as termites, ants and other boring insects. As used herein, the term xe2x80x9cbioactivexe2x80x9d means stimulating an organism, usually in a negative way up to and including death for purposes of a deterrent.
Wood which is in contact with concrete, such as in wooden building construction and wood which is in contact with soil for example fence posts, utility poles, railroad cross-ties and wooden supports, can be structurally degraded by the action of termites, ants and other boring insects. Insecticides are available to protect wood from the action of such pests.
In wooden building construction, wood in contact with concrete may be structurally degraded by action of one or more wood pests including but not limited to termites, ants and other boring insects. Present methods of preventing or retarding the advance of insects includes fumigation wherein the entire structure may be sealed and an insecticide released therein. Disadvantages of this method include ecological and human health concerns as well as the limited time until the fumigant is sufficiently reduced in concentration to permit insect ingress.
Although insecticides are effective against the action of the boring insects, the insecticides must be repeatedly applied at intervals of from a few days to a few months or a year to remain effective. If insecticides are applied by themselves in sufficient quantity to be effective over a period of time, they pose ecological concerns, human health, and may present unpleasant odors, soil leaching and volatility of the insecticide. Furthermore, even the greatest amounts of insecticides applied by themselves dissipate within a relatively short time and need to be reapplied.
A further disadvantage of conventional application methods is that the concentration of bioactive ingredients resulting from a single application of insecticide starts out well above the minimum level necessary for effectiveness, but decreases rapidly and within a relatively short period of time drops below the minimal effective level necessary to maintain a barrier.
To this end, a number of techniques for the controlled release of chemicals such as insecticides have been developed in recent years. These methods employ polymer matrices and microcapsules to release insecticide.
Cardarelli U.S. Pat. No. 4,400,374 discloses the use of polymer matrices generally made of polyethylene, polypropylene, ethylene vinyl acetate, polyamide, polystyrene, polyvinyl acetate, or polyurethane to control the release of insecticides such as the insecticide commercially available under the tradename Dursban. The polymer matrices disclosed in U.S. Pat. No. 4,400,374, incorporate porosigen and a porosity reducing agent which upon contact with soil moisture or an aqueous environment dissolves the matrix.
Similarly, Cardarelli U.S. Pat. No. 4,405,360 relates to a polymer release matrix which can be composed of polyamide, polyurethane, polyethylene, polypropylene, polystyrenes and other polymers. The control release mechanism works in combination with a porosigen to release a herbicide in a moist environment.
A disadvantage of the Cardarelli methods is the necessity of sufficient moisture to dissolve the matrix. Periods of dryness, while extending the life of the matrix, would result in a decrease in the insecticide concentration thereby permitting access to the insects. In addition, the longevity of the matrix is variable and dependent upon moisture content.
In addition, Wysong U.S. Pat. No. 4,435,383 teaches the use of a controlled release mechanism for insecticides including carbamates, organothiophosphates, organophosphates, perchlorinated organics and synthetic pyrethroids. The release mechanism comprises a hydrophobic barrier monomer namely styrene and/or methyl styrene in combination with a monomer selected from one or more unsaturated mono- or di-carboxylic acids.
Another reference, Tocker U.S. Pat. No. 4,282,209 discusses a process for the preparation of insecticide-polymer particles. The insecticide, methomyl, is used to control insects which attack a tobacco, cotton or agricultural crops. Methomyl is dissolved with polymers such as polyamides, urethanes and epoxies to provide extended residual insecticidal activity.
A second Tocker patent, U.S. Pat. No. 4,235,872, discloses the use of slow-release insecticide microcapsules having a core of methomyl surrounded by a cover of allaromatic, uncrosslinked polyurea. In the arrangement disclosed in this patent, methomyl is used to protect vegetables, field crops and fruit crops.
A sixth reference, Young et al. U.S. Pat. No. 4,198,441, discloses the use of insecticides such as Dursban in a controlled release matrix comprising an organopolysiloxane, a hydrolyzable silane and a hydrolyzable organic titanium.
Additionally, Young et al. U.S. Pat. No. 4,160,335 discloses a mode of dispersing insect control substances by applying stripes to sheets of cellophane. The insect control substance which can include Dursban is placed in a polymer as well.
Another method is described in an Australian patent AU-B-82443/91. In this patent, there is described two sheets of plastic drawn from supply rolls. The upper face of the lower sheet and the lower face of the upper sheet are drawn past respective coating rollers which apply a coating of pesticide (e.g. permethrin) in a volatile solvent to the faces of the sheets. The coated faces of the sheets are brought together by passing them between compressive rollers. The coated and pressed sheets are laid under building foundations, or placed around trees or plants to prevent termite attack. Disadvantages of this product and method include (1) severance of a layer permits rapid escape of the coating, and (2) the coating is not integral to the sheets thereby permitting faster diffusion through the sheets and limiting the effective life.
Coated granules have a pesticide absorbed onto a matrix such as clay and then coated with cross-linked resins which helps slow the release rate. Clay loses or releases pesticide over a short period of at most a few weeks.
Although the prior art does disclose the use of an insecticide incorporated into a polymer matrix as controlled release agents, none of the references teach the creation and maintenance of a completely effective exclusion zone lasting several years or more. It is desirable to create a zone so as to prevent any contact between the wood structure and insects capable of damaging such structures. A reliable exclusion zone is necessary to protect wood structures for periods of time substantially greater than one year.
Therefore, in view of the above, it is an object of this invention to provide a zone of insecticide to protect wooden structures. Such zone consisting of a long term low volatility barrier and a high volatility short term barrier to protect soil.
It is a further object of this invention to maintain an exclusion zone for relatively great lengths of time of about 10 to 20 years.
The present invention is a wood pest barrier having a lifetime that is effective over the life of the structure. The lifetime is achieved by binding the pesticide within the polymer matrix thereby substantially preventing release of the pesticide from the polymer. Binding may be achieved by mixing the pesticide with a carrier as a bound friable mix prior to placing the bound friable mix within the polymer matrix.
The barrier may be supplemented with additional layer(s) including but not limited to scrim, mesh, sheet, and combinations thereof. The additional layer(s) may contain a second pesticide that is the same or different compared to the pesticide in the barrier. In addition, the second pesticide may be permitted to release from the additional layer(s) for enhanced short term protection.
The barrier and/or additional layer(s) are made with a polymer selected from the group consisting of thermoplastic polymers, thermoset polymers, elastomeric polymers and copolymers thereof. By incorporating the insecticides into the polymers, the insecticides can be held or released at such a rate that they will continue to be effective as toxicants or repellents for insects capable of damaging wood structures for a prolonged period of time while at the same time maintaining sufficient concentrations within the barrier to prevent insect penetration through the barrier.
According to one aspect of this invention, there is provided a polymeric-carrier system wherein the pesticide is bound to the carrier as a bound friable mix. The sheeting with the bound friable mix is then placed near a wooden structure to provide a barrier that wood pests do not penetrate. An additional layer may provide means for a slow and relatively constant release of the volatile insecticide in order to create a barrier zone beyond the barrier itself in the soil around a wood structure. The polymers include thermoplastic polymers, thermoset polymers, elastomeric polymers as well as copolymers thereof and the insecticide comprises the family of insecticides known as pyrethrins.
According to another aspect of this invention, an exclusion zone is created by placing an extrusion near the wooden structure to be protected. The extrusion has a polymeric delivery system capable of controlled release of the insecticide. The carrier system maintains a steady and effective concentration of insecticide in the exclusion zone for great lengths of time.
According to another aspect of this invention, a pellet comprising a polymer and insecticide is provided to create and maintain an equilibrium concentration of insecticide for ants, termites and other wood boring insects in an exclusion zone for the wooden structure. The pellet is placed near a wooden structure to treat the soil in order to shield the wooden structure from termites, ants and other boring insects. The pellet can be placed near the structure by a variety of means. Additionally, the pellet can be embedded in a board or even included in a foam. In preferred embodiments the polymers include thermoplastic polymers, thermoset polymers, elastomeric polymers as well as copolymers thereof and the insecticide are pyrethrins.
According to another aspect of this invention, an exclusion zone is created by injecting a hot melt polymeric mixture. The controlled release device comprises one or more pyrethrins and the polymer is selected from the group consisting of thermoplastic polymer, elastomeric polymers and copolymers thereof.
According to further aspects of the invention, temperature driven controlled release devices are used to provide the exclusion zones.
According to another aspect of this invention, the controlled release device is used to fumigate structures.
It is desirable to place a barrier or create a zone so as to prevent any contact between the wood structure and insects capable of damaging such structures. An exclusion zone is necessary to protect wood structures for extended periods of time.
In a further aspect of the present invention a high density polymer having a low volatility insecticide providing a low release rate of insecticide is combined with a low density (soft) polymer having a more volatile insecticide to provide a reliable exclusion zone.
Therefore, in view of the above, it is an object of this invention to provide a barrier of insecticide to protect wooden structures.
It is a further object of the present invention to provide a barrier and an exclusion zone having of a long term low volatility barrier and a high volatility short term barrier to protect adjacent soil.
It is a further object of this invention to maintain a barrier for relatively great lengths of time or about 10 to 20 years.